Printing is a manufacturing process. The profitability of a printing operation is tied closely to production throughput. The faster a printer can produce quality ink on paper, the more profit can be generated. A major barrier to faster print production lies in the pre-press department. Even in the nearly digital filmless environment of computer-to-plate imaging, it takes a significant amount of time to image plates for commercial quality printing. Speeding up the plate manufacturing process would offer a variety of benefits. Faster plate production can result in greater output, increased plate setter utilization and increased press utilization.
In the world of digital imaging, a gray level is typically represented by a value from 0-255. 256 shades of gray are usually considered sufficient to represent realistic images. In the printing industry shades of gray are implemented by modulating the size of screen dots. Screen dots are imaged at different frequencies and angles. The angles are associated with ink color and the frequencies are used to achieve image quality. Typically the higher the frequency, the better the quality of printing.
A screen dot in the digital world is composed of microdots or pixels. An array of these pixels is used to create a printing screen dot. An array of 16.times.16 pixels is needed to represent 256 shades of gray. A pixel is tied to the imaging resolution of a device that creates film or plate for the printing process. Some devices support multiple resolutions. For example, there are imaging devices with 1000, 2000, and 4000 pixels per inch. At lower resolutions, it is impossible to support high screen frequencies while maintaining a high number of gray shades. At 1000 ppi, a 16.times.16 pixel array can support only 62.5 line per inch screen. This screen frequency is not good enough for typical color printing work.
In order to increase the screen frequency, printers are forced to image film and plate at higher resolutions. While this achieves the desired quality, it also slows production. For example, a plate imaged at 2000 ppi will take twice as long to image as one done at 1000 ppi.
Another approach besides increasing resolution is to sacrifice the number of shades of gray that can be attained with a certain cell size. A cell size of 10.times.10 will provide 100 shades but will yield a screen of only 100 lines per inch at 1000 ppi. In order to achieve screen frequencies in the range of 140+1 pi we need cell sizes on the order of 6.times.6. The number of shades of gray achievable with this approach is well below an acceptable amount.